Current endovascular procedures to treat vascular diseases use a variety of metallic devices, e.g., guidewires, stents, filters, cage-like vascular plugs, and coils. One of the most popular materials used for the endovascular metallic devices is NiTi/Nitinol, so called shape memory alloy. Although endovascular devices made of NiTi demonstrate a great performance in human vessels, there are several intrinsic limitations. Another common metallic material for endovascular device is Cobalt-Chromium alloy (CoCr), which is often used for stents.
First limitation is a friction between a metallic device and catheter. A metallic device is inserted into a plastic catheter, and is pushed out or twisted in the catheter. In order to reduce the friction, the inner lumen of catheter or the surface of some metallic guidewire has a hydrophilic polymer coating. However, such a hydrophilic coating is not enough to overcome this limitation. The hydrophilic polymer coating comes off from the device relatively easily. Also certain devices such as a stent are not easily coated with the hydrophilic polymers. In fact, most stents are not coated with hydrophilic materials. The friction makes the delivery of stent or coil into a target lesion difficult and unsafe. Furthermore, the friction makes it difficult to design a longer stent because a longer stent would induce an increase in friction so as to be difficult to deliver to a target lesion. The friction also makes it difficult to control (twist and push/pull) a metallic guidewire.
The second limitation is that a patient who receives an intra-arterial metallic device placement, particularly a metallic stent placement, is required to be medicated with anti-platelet medications such as Aspirin or Plavix, so called blood thinners, for several months in order to prevent clotting and occlusion of stent lumen. The blood thinners itself carry a risk of spontaneous bleeding in organs such as brain and gastrointestinal tract. Even with the blood thinning medications, the clotting of important arteries occurs not infrequently after the placement of metallic devices in the vessels since the devices are a foreign material for the human vessels. Although the clotting due to the intravascular metallic device placement involves a complex multi-factorial processes, inflammatory reaction and vascular injury are important factors that activate the coagulation cascade. Furthermore, the metallic device should be covered with native tissues and cells in the healing process so that the foreign material does not have a direct exposure to blood flow.
Therefore, there is a need for an endovascular device having an enhanced rate of endothelialization and/or neointima coverage as well as an enhanced affinity of the device with a native vascular tissue. An enhanced rate of endothelialization and/or neointima coverage would allow sooner cessation of blood-thinning medications so as to reduce or minimize the risk of spontaneous bleeding in organs such as brain and gastrointestinal tract.
The embodiments described below address the above identified problems and needs.